1. Field of the Invention
The present invention relates to a laminate and a process for producing it, and more specifically relates to a laminate which comprises a non-oriented polyphenylenesulfide film and a biaxially oriented polyphenylenesulfide film whose main components are polyphenylenesulfide (hereinafter, this term is also referred to as "PPS").
2 Description of the Prior Art
Electrical insulating materials, having various properties such as heat resistance (particularly, long-term heat resistance under a high-temperature condition), electrical properties, mechanical properties (particularly, impact resistance) and flame resistance with a good balance and further having an excellent processability (particularly, a high tear strength capable of preventing a material from being broken), have been required accompanying with miniaturization and elevation of efficiencies of electrical equipments or parts for vehicles.
For example, the following materials are known as the conventional electrical insulating materials used in such technical fields.
(1) a biaxially oriented PPS film disclosed in, for example, Japanese Patent Laid-Open SHO 55-35459
(2) non-oriented PPS sheets disclosed in, for example, Japanese Patent Laid-Opens SHO 56-34426 and 57-121052
On the other hand, laminated films and laminates such as the following ones are also known.
(3) a laminate formed by laminating biaxially oriented PPS films to each other via an adhesive disclosed in, for example, Japanese Patent Laid-Open SHO 61-241142 (it is also known that biaxially oriented PPS films are heat stacked to each other by surface treatment such as corona discharge treatment or plasma treatment.)
(4) a laminate formed by laminating a biaxially oriented PPS film and a biaxially oriented polyester film disclosed in, for example, Japanese Patent Laid-Open SHO 62-292431
(5) a laminate formed by laminating a biaxially oriented PPS film and a fibrous sheet composed of an aromatic polymer disclosed in, for example, Japanese Patent Laid-Open SHO 60-63158
(6) a laminate formed by laminating a biaxially oriented PPS film and an ethylene tetrafluoride-propylene hexafluoride copolymer filmdisclosed in, for example, Japanese Patent Laid-Open SHO 62-292432
(7) a laminate formed by laminating a biaxially oriented PPS film and an injection molded PPS plate disclosed in, for example, Japanese Patent Laid-Open HEI 1-192547
However, such conventional film, sheets and laminates have the following problems.
The film of the above (1) has a poor impact resistance and a poor tear strength. Therefore, for example, when the film is used as a slot liner or a wedge of a motor, the film is easily torn or delaminated.
Although the non-oriented sheet of the above (2) has a high tear strength, it has a low tensile elongation. Moreover, when the sheet is exposed in a high-temperature condition near its melting point, its mechanical properties are rapidly decreased and its stability in shape is remarkably deteriorated because the sheet has a poor long-term heat resistance. Therefore, it is difficult to use the sheet as an electrical insulating material by itself.
The laminate of the above (3) has higher impact resistance and tear strength as compared with the film of the above (1), but it is not sufficient. Moreover, since an adhesive interposes between the laminated films, it is liable to occur that the excellent properties of the biaxially oriented PPS films such as heat resistance and chemical resistance are decreased. In the laminate wherein biaxially oriented PPS films are heat stacked to each other, the adhesive property of the laminate is poor and the laminate is easily delaminated by applying an impact force.
In the laminate of the above (4), since the heat resistance, chemical resistance and wet heat resistance of the biaxially oriented polyester film, which constitutes a main layer, are poor, the excellent properties of the biaxially oriented PPS film cannot be realized, and there is a limit for use of the laminate.
Although the laminate of the above (5) has a high impact resistance, because lamination is performed via an adhesive and the adhesive cannot have high heat resistance and chemical resistance, the properties of the laminate are decreased as a whole. Moreover, since the hygroscopic property of of the fibrous sheet of the laminate is very high, the dimensional change under a wet heat condition of the laminate is large. Furthermore, the fibrous sheet of the laminate gets loose and chips are generated, when the laminate is processed in, for example, slitting process. Therefore, this laminate is restricted in use for an insulating material of an electrical equipment which requires a high accuracy, for example, a hermetic motor for a refrigerator.
In the laminate of the above (6), the laminate has high heat resistance and chemical resistance, and because the films are laminated without using an adhesive, there is not a fear that an adhesive give a bad influence to the laminate. However, various surface treatments for the films are required to make the laminate. In addition, since the adhesive force at the laminated surfaces in the laminate is weak, the films are easily delaminated and the biaxially oriented PPS film is easily torn when an impact force is applied to a part of the laminate.
In the laminate of the above (7), as the injection molded PPS plate is crystallized, there is a problem similar to that in the film of the above (1).
On the other hand, it has been required more and more to increase the impact resistance and tear strength of a laminate while maintaining the excellent properties of biaxially oriented PPS film.